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I have a dual-dipole antenna with a subreflector slightly above it and a ground plane below it, and attached to the ground plane is a balun. While simulating in CST microwave studios, I didn't include a balun. I'm wondering how excluding the balun might affect the s-parameters, beam patterns, etc.

Any help would be appreciated!

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  • $\begingroup$ Is the feedline coming up, through the ground plane? If so, and assuming an ideal ground plane, the feedline is screened from any fields around the antenna and I can't see how a balun would make a difference. $\endgroup$ – Phil Frost - W8II Jan 12 '17 at 18:21
  • $\begingroup$ Yes the feedline comes up through the balun, then through the groundplane. Could lack of a balun be responsible for impedance mismatch in my smith chart by chance? $\endgroup$ – boson Jan 13 '17 at 1:41
  • $\begingroup$ If it's not a 1:1 balun, I suppose so. $\endgroup$ – Phil Frost - W8II Jan 17 '17 at 13:27
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The question has not been answered and although somewhat dated, I thought I would provide some feedback.

A balun can affect all four scattering parameters. The transformation ratio, the feed characteristic impedance, and the complex load impedance all play a role. It must also be acknowledged that most real world baluns do not perform a linear translation for all complex impedances. This non linearity is difficult to effectively model.

Regarding the "beam pattern", perhaps better described as directivity, can be affected by the balun if the balun effectively prevents common mode currents on the feedline. But to see this effect, the model would need to anticipate radiation (or pickup) by the feedline. This is rarely the case unless the engineer has taken care to build this possibility into the model.

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